1. Field of Invention
The present invention relates to a power supply for a display monitor; and more particularly relates to a high efficiency Switching Mode Power Supply (SMPS) apparatus with a Power Factor Correction circuit (PFC).
2. Description of Related Art
Traditionally, a PFC circuit is used in devices with high wattage, which improves the power of an alternating-current transmission system so the voltage and the current are substantially in phase. But an increasing number of personal computers (PCs) having display monitors provide a remarkable potential for saving power by equipping the display monitors with a PFC circuit. Display monitors may also include other display devices which can be connected to a mains voltage and based for instances on cathode ray tube, liquid crystal or projection type display technology.
It is known in the art to use a separate PFC circuit between a mains outlet and a power consuming device. For example, EP 0 673 106 A1 discloses circuits for achieving a higher power factor in a switched mode power supply. FIG. 2 of EP 0 673 106 A1 shows a circuit having a step-up regulator arranged between a bridge-type rectifier and an AC energy distribution source that includes a capacitor C, a transformer M, a controller CTRL1, a switch S1, a diode D2 and a capacitor C2. One disadvantage in the related art is that the PFC circuit is always ON when main voltage is available. The reader is also referred to a technical disclosure by Siemens identified as the TDA 4862 datasheet.
It is also known in the art to add a PFC module, as such, inside a housing of such a power consuming device.
There is a need in the art to develop a cooperation between a display monitor and a PFC circuit in order to improve the efficiency of a power supply and power saving.
Moreover, many display monitors have a universal power supply, i.e., the same power supply is able to operate with a large value of the mains voltages for instance in US (110V) and in Europe (230V). Display monitors also have power saving properties. Display monitors are automatically switched to a power save state after inactivity of the user.
There is a need in the art to: (1) equip such display monitors power supplies with a PFC circuit which are also universal, i.e., properties of a PFC circuit are controlled according to the operating situation; (2) make a PFC circuit controllable according to mains voltage of display monitor; (3) make a PFC circuit controllable according to power consuming of a display monitor; and (4) find an economical solution where additional control circuitry for the PFC circuit is minimized by sharing an existent display controller for controlling power factor correction.
Moreover, PFC circuits known in the art provide a load with a fixed and regulated voltage that equals the mains voltage type. Regulated PFC output voltage is typically 400V in Europe (mains 230V) and 230V in US (mains 110V). In the art, universal monitors which cover both mains voltage types are working typically with a mains voltage range of 90V,. . . , 265V. The problem with fixed regulated PFC output voltages is the voltage gap between input voltage (the mains voltage) and output voltage. High voltage gap with high peak currents in inductor and switch increases losses in those components. Minimizing the voltage gap decreases losses in the inductor, switch and rectifier. This would allow a smaller and lighter inductor and switch, which would result in cost reductions.